Optimal resource allocation for cooperative cognitive radio networks with opportunistic access to the licensed spectrumis studied.\r\nResource allocation is based on minimizing the symbol error rate at the receiver. Both the cases of all-participate relaying and\r\nselective relaying are considered. The objective function is derived and the constraints are detailed for both scenarios. It is then\r\nshown that the objective functions and the constraints are nonlinear and nonconvex functions of the parameters of interest, that\r\nis, source and relay powers, symbol time, and sensing time. Therefore, it is difficult to obtain closed-form solutions for the optimal\r\nresource allocation. The optimization problem is then solved using numerical techniques. Numerical results show that the allparticipate\r\nsystem provides better performance than its selection counterpart, at the cost of greater resources.
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